Method of manufacturing a polymeric foil

ABSTRACT

Applying the method of manufacturing a polymeric foil ( 30 ) having partly embedded inorganic particles ( 19 ) results in the polymeric foil ( 30 ) being suitable for use as a movable element ( 3 ) in a display panel ( 21 ). The method starts by embedding inorganic particles ( 19 ) partly into a release layer ( 32 ) which covers a substrate ( 31 ). This product ( 37 ) is covered with a layer of polymeric material ( 18 ), which is solidified to obtain the polymeric foil ( 30 ). By removing the release layer ( 32 ), the polymeric foil ( 30 ) having a surface with a roughness brought about by the partly embedded inorganic particles ( 19 ) is set free.

The invention relates to a method of manufacturing a polymeric foilhaving partly embedded inorganic particles, the polymeric foil beingsuitable for use as a movable element in a display panel.

A display panel having such a polymeric foil is known fromPHNL010908EPP. The known display panel comprises a light guide plate inwhich, in operation, light is generated and trapped so that this firstplate forms a light guide, a second plate and, between said two plates,a movable element. By applying voltages to electrodes on the light guideplate and the second plate, and to the movable element, which is madefrom conductive material or contains a conductive layer, the movableelement is locally brought into contact with the light guide plate orthe second plate. At locations where the movable element is in contactwith the light guide plate, light is coupled out of the light guideplate. A roughness brought about by partly embedded inorganic particles,hereinafter also called inorganic protrusions, is present at the surfaceof the movable element facing the light guide plate for contacting thelight guide plate. The display panel requires relatively little energyto interrupt the physical contact between the movable element and thelight guide plate by applying voltages to the electrodes and the movableelement, while good optical contact can still be provided between themovable element and the light guide plate.

For the production of the known display panel on an industrial scale,there is a need for the polymeric foil in relatively large amounts.Experiments have been carried out to find a manufacturing method that isapplicable on an industrial scale. In an experiment a dispersion ofinorganic particles in a solution containing a solvent and a polymericsolute was applied as a polymer/particle/solvent layer to a substrate,after which the solvent was removed. Then the resulting polymeric foilwas removed from the substrate. The polymeric foil had a roughness atthe surface facing the substrate comparable to the roughness of thesurface of the substrate facing the polymeric foil, but contained hardlyany inorganic protrusions at the surface. In another experiment, where asolution containing a solvent and a polymeric solute was applied as apolymer/solvent layer to a substrate, inorganic particles were depositedon top of the solvent/solute layer while removing the solvent from thislayer. The resulting polymeric foil contained more inorganic protrusionsat the surface facing away from the substrate. However, thereproducibility of the distribution of the inorganic protrusions at thesurface and the adjustability of the surface roughness by the method ofmanufacturing were low.

A drawback of these methods of manufacturing a polymeric foil is that inthis way it is difficult to manufacture the polymeric foil with areproducible distribution of the inorganic protrusions at the surface ofthe polymeric foil, and with a surface roughness that is relatively welladjustable. Therefore these methods are little suitable for theproduction of the polymeric foil on an industrial scale.

It is an object of the invention to provide a method of manufacturing apolymeric foil of the type mentioned in the opening paragraph, which isapplicable on an industrial scale.

The object is achieved by the method comprising the steps of

-   a) embedding inorganic particles partly into a release layer which    covers a substrate, thereby obtaining a product having a rough    surface,-   b) covering the product with a layer of polymeric material, thereby    partially embedding the inorganic particles within the layer of    polymeric material,-   c) solidifying the layer of polymeric material to obtain the    polymeric foil, and-   d) removing the release layer to set free the polymeric foil having    a surface with a roughness brought about by the partly embedded    inorganic particles.

The inventors have realized that the process of making the inorganicprotrusions has to take place in one or more well controllable steps.For this purpose a release layer is used, in which inorganic particlescan be partly embedded. The process of embedding the inorganic particlespartly into the release layer is well controllable by choosing thediameter of the inorganic particles to be such that it is larger thanthe thickness of the release layer, and by choosing the release layermaterial such that the inorganic particles are embedded into the releaselayer when the release layer exists in, or is brought into, a relativelysoft viscous state. The inorganic particles are embedded in the releaselayer until they are at rest at the interface between the release layerand the substrate. The resulting product has a rough surface, which issubsequently covered with a layer of polymeric material. The inorganicparticles that are partly embedded in the release layer are also partlyembedded in the layer of polymeric material. By subsequently solidifyingthe layer of polymeric material, the polymeric foil is obtained. Theinorganic particles are partially embedded in the solidified polymericmaterial. After removal of the release layer, the inorganic particlesare still partially embedded and thus trapped in the polymeric material:the polymeric foil is set free from the substrate and has a surface witha roughness brought about by the organic particles partly embeddedtherein. The surface roughness can be controlled by the thickness of therelease layer, the diameter of the inorganic particles and the surfacenumber density of the inorganic particles in direct contact with therelease layer and by controlling the step of embedding the inorganicparticles partly into the release layer.

In this way a polymeric foil is manufactured with a reproducibledistribution of the inorganic protrusions at the surface of thepolymeric foil and with a surface roughness that is relatively welladjustable. Therefore this method is applicable for production of thepolymeric foil on an industrial scale.

It is important that, when the inorganic particles contact the releaselayer, the release layer used is brought into a relatively soft viscousstate for embedding inorganic particles partly into the release layer.If the release layer is not already in a relatively soft viscous stateit has to be brought into that state. For example, the release layer isbrought into a relatively soft viscous state by raising the temperatureof the release layer above a softening temperature of the release layer.Alternatively, the release layer is brought into a relatively softviscous state by bringing the release layer into contact with a materialthat is a solvent for the release layer, for example if the releaselayer used contains organic material. In a particular example, therelease layer used contains water-soluble organic material. Furthermore,use of a release layer containing water-soluble organic material has theadvantage that the step of removing the release layer to release thepolymeric foil from the substrate can be performed by dissolving therelease layer in water. In a preferred embodiment the release layer isbrought into a relatively soft viscous state by exposure of the releaselayer to moist air. This is attained in a controllable way by exposingthe release layer during a controlled period of time to a controlledhigh-humidity environment wherein the relative humidity is in the80%-100% range. The water vapor softens the release layer for embeddingthe inorganic particles partly into the release layer. The inorganicparticles remain partly embedded in the release layer after removal ofthe product from the high-humidity environment. In an even morepreferred embodiment the release layer used contains polyvinyl alcohol.Polyvinyl alcohol is a versatile water-soluble organic materialavailable in a wide variety of molecular weights and chemicalcompositions and is an excellent film former. It can be readilydeposited as a polyvinyl alcohol/water film in a variety of thicknessesacross the substrate, e.g. by spin coating of a polyvinyl alcoholsolution in water across the substrate, and forms a hard release layerwhen the water is removed from the cast film. A polyvinyl alcoholrelease layer softens when exposed to a relatively high-humidityenvironment and is environmentally friendly.

A wide range of dimensions of the inorganic particles is possible.Inorganic particles having a diameter smaller than the thickness of therelease layer can penetrate completely into the release layer during theembedding process. They will not add to the surface roughness of thepolymeric foil as they will not become partly embedded into thepolymeric foil, and they are removed when the release layer is removedto set free the polymeric foil. The combination of the release layerused having a thickness between 5 and 100 mm, and the inorganicparticles used having a diameter larger than the thickness of therelease layer results in a polymeric foil with a surface roughness inthe range in between 5 and 100 nm brought about by inorganicprotrusions. This is the preferred range for the roughness of thesurface of the polymeric foil facing the light guide plate. Theinorganic protrusions do not readily undergo elastic and/or plasticdeformations when the movable element is in contact with the light guideplate. The roughness is large enough to substantially reduce theadhesive Van der Waals' forces, resulting in a display panel requiringrelatively little energy to interrupt the contact between the lightguide plate and the movable element. On the other hand, the surfaceroughness is small enough to ensure that light can be satisfactorilycoupled out of the light guide plate and coupled into the polymericfoil. In a preferred embodiment inorganic particles used have a diameterbetween 100 and 1000 nm. The obtained polymeric foil has a surfaceroughness in the preferred range whereas the inorganic particles havedimensions which are smaller than the thickness of the polymeric foil,which is generally in the range between one and two micrometers.Inorganic particles can also be fully embedded within the bulk of thepolymeric foil. In that case, these particles are referred to asscattering particles: these particles are present to scatter light outof the polymeric foil. It is even possible that the inorganic particlesrepresenting the scattering particles are of a different size ormaterial than the inorganic particles forming the inorganic protrusions.In that case, step b) is extended with an extra deposition step of theother type of inorganic particles.

In step a) the inorganic particles are deposited on the release layer.This deposition can be performed in several ways, for instance theinorganic particles are deposited on the release layer as aparticle/solvent film using a wet coating technique, such as spincoating, dip coating, spray coating, or curtain coating of aliquid-based inorganic particle dispersion across the release layer. Theinorganic particles take the form of an inorganic particle layer on therelease layer following the removal of the solvent from theparticle/solvent film. Alternatively, in step a) the inorganic particlesare deposited from an aerosol phase. Then the inorganic particles areblown as aerosolized particles in air towards a release layer. Inorganicparticle deposition from an aerosol phase is an environmentally friendlyprocess step and allows a relatively good homogeneity of the depositedinorganic particle layer to be attained across the release layersurface. The characteristics of an aerosol deposition step involve thedispersion of a particle powder in air, hereinafter referred to as aparticle aerosol, and the classification of the particle aerosol intoparticles having a diameter that falls within a desired range. Forobtaining a particularly homogeneous distribution of inorganic particlesacross the release layer, in step a) the inorganic particles arepreferably deposited from an aerosol phase by using gravity depositionor electrostatic deposition. Gravity deposition of inorganic particleson the release layer is obtained by allowing the classified inorganicparticle aerosol to be homogeneously present throughout the volume of asettling chamber and to settle from the aerosol phase onto the releaselayer during a controlled period of time under the influence of theforce of gravity acting on the aerosolized inorganic particles.Electrostatic deposition of inorganic particles on the release layerinvolves the electrostatic charging of the classified inorganic particleaerosol through either a corona charging step or a tribo charging stepor a mixed corona/tribo charging step, the transport of the chargedinorganic particle aerosol towards the release layer, and theelectrostatic deposition of the charged inorganic particle aerosol ontothe release layer under the influence of an electrostatic potentialdifference between an electrode and the substrate. A definedelectrostatic potential can be imposed on the substrate when thesubstrate used has a conductive layer or when a conductive layer ispresent in close proximity to the substrate at the side of the substratefacing away from the release layer.

The deposition of inorganic particles from an aerosol phase onto arelease layer frequently results in an inorganic particle layercharacterized by an open fractal-like inter-particle structurepossessing a large porosity and a small particle volume fraction. Thevolume fraction of the inorganic particle layer on the release layer isincreased if between step a) and step b) the product is immersed in andsubsequently withdrawn from a liquid for increasing the volume fractionof the inorganic particles on the release layer. This dipping processinvolves the immersion of the product into a dipping liquid followed bythe withdrawal of the product from the dipping liquid. For the dippingliquid use is preferably made of a liquid that is a non-solvent for therelease layer material and that wets the deposited inorganic particles.An example of a preferred dipping liquid is heptane if the release layermaterial is polyvinyl alcohol and the inorganic particles are TiO₂.

In step b) the product can e.g. be covered with a polymeric material byusing a wet coating method such as spin coating, dip coating, spraycoating or curtain coating the polymeric material being dissolved ordispersed in a solvent. The wet coating method initially covers theproduct with a polymer/solvent film. Solidifying the polymeric materialin step c) occurs during removal of the solvent from the polymer/solventfilm. An additional annealing step or curing step at a high temperaturemay be necessary or desirable to further improve the solidification ofthe polymeric material. Alternatively, in step b) the product can becovered with a polymeric material such as parylene using a solvent-freevapor deposition polymerization of parylene monomers, for exampleaccording to the Gorham process. Polymerization and solidification ofthe parylene layer occurs simultaneously with the deposition of theparylene monomers on the product.

The solidified polymeric material exists either in a glassy amorphousstate or in a crystalline state or in a mixed glassyamorphous/crystalline state, for example, to give the solidifiedpolymeric material a stiffness similar to that of a crystalline organicmaterial. These materials are not readily subject to plastic deformationand/or creep.

To apply a voltage to the polymeric foil, the polymeric foil must haveconductive properties. These are provided if the polymeric material is agood conductor. If the polymeric material is not a good conductor, suchas for example parylene, polymethylmethacrylate, some fluoropolymers andpolyimide, in the method of manufacturing the polymeric foil anadditional step is performed in which the product and/or the polymericfoil is covered with a conductive layer prior to performing step d).This additional process step results in three different polymeric foils.If the product is covered with a conductive layer prior to performingstep d), the polymeric foil used as a movable element has the conductivelayer at the surface facing the light guide plate. If the polymeric foilis covered with a conductive layer prior to performing step d), thepolymeric foil used as a movable element has the conductive layer at thesurface facing the second plate. If the product is covered with a firstconductive layer and the polymeric foil is covered with a secondconductive layer prior to performing step d), the polymeric foil used asa movable element has a first conductive layer at the side facing thelight guide plate and a second conductive layer at the side facing thesecond plate. Alternatively, the polymeric foil can be covered withconductive layers on one or on both sides after the foil is set freefrom the substrate. Due to the conductive layer or layers, the polymericfoil contains an electrode for applying voltages. An advantage of havingconductive layers on both sides of the polymeric foil is that a singlepotential can be applied to both conductive layers, which results in apolymeric foil potential that is uniformly present throughout the entirepolymeric foil volume. This uniform potential prohibits the developmentof static charge formation on the polymeric foil surface or within thepolymeric foil. The conductive layers are preferably opticallytransparent and inorganic in nature. An example of a preferredconductive layer is an indium-tin-oxide layer.

In the method of manufacturing the polymeric foil an additional step maybe performed in which the product and/or the polymeric foil is coveredwith an inorganic layer prior to performing step d). Alternatively, thepolymeric foil can be covered with an inorganic layer on the side facingthe light guide plate and/or on the side facing the second plate afterthe polymeric foil is set free from the substrate. The advantage ofhaving an inorganic layer on one side or on both sides of the polymericfoil is that the inorganic layer increases the stiffness and wearresistance of the polymeric foil surface. An increased stiffness of thepolymeric foil surface counteracts creep and visco-elastic and/orplastic deformations of the polymeric foil surface, which is desirableto diminish the chance of strong adhesive forces from ever occurringbetween the polymeric foil and the light guide plate or between thepolymeric foil and the second plate. An increased wear resistance givesprotection against possible gradually occurring damage to the polymericfoil surface when the polymeric foil is used as a movable element in adisplay panel.

A roughness of the surface of the polymeric foil facing the second platein the range between 100 and 1000 nm results in a display panelrequiring relatively little energy to interrupt the contact between thesecond plate and the movable element. However, after performing step c)and prior to performing step d) the roughness of the polymeric foil canfall outside this range. For this reason, the polymeric foil has a freesurface facing away from the release layer, which surface is treated toadjust the surface roughness so as to be within a range between 100 and1000 nm prior to performing step d). This surface treatment can be asmoothing or roughening step, for instance through chemical etching,polishing or rubbing. Another treatment that smoothens the secondsurface of the polymeric foil involves spin coating or dip coating of apolymer/solvent film across the polymeric foil from a polymer solutionfollowed by solvent removal. In this way, the roughness of the secondsurface of the polymeric foil facing the second plate can be adjusted soas to be in said range.

These and other aspects of the invention will be further elucidated anddescribed with reference to the drawings, in which:

FIG. 1 shows schematically a cross sectional view of the display panel,

FIG. 2 shows schematically a part of the display panel,

FIG. 3 shows schematically the polymeric foil,

FIG. 4 shows schematically the steps in the method of manufacturing thepolymeric foil,

FIG. 5 shows schematically two embodiments of the substrate usedcontaining a conductive layer,

FIG. 6 shows schematically the steps in the dipping and immersionprocess,

FIG. 7 shows schematically a first example of the steps of depositing aconductive layer,

FIG. 8 shows schematically a second example of the steps of depositing aconductive layer, and

FIG. 9 shows schematically the steps of depositing two conductivelayers.

The figures are schematic and not drawn to scale, and in all the figureslike reference numerals refer to corresponding parts.

In FIG. 1 the display panel 21 comprises a light guide plate 2, amovable element 3 and a second plate 4. Electrodes 5 and 6 are arranged,respectively, on the sides of the light guide plate 2 and the secondplate 4 facing the movable element 3. The display panel 21 comprises acovering element 7 connected to the light guide plate 2, thus forming aspace 8. The display panel 21 further comprises a light source 9. Lightgenerated by the light source 9 is coupled into the light guide plate 2.The light travels inside the light guide plate 2 and, due to internalreflection, cannot escape from the light guide plate 2 unless thesituation as shown in FIG. 2 occurs. In FIG. 2 the movable element 3locally lies against the light guide plate 2. In this state, part of thelight enters the movable element 3. The movable element 3 couples thelight out of the light guide plate, so that it leaves the display panel21. The light can issue on both sides or on one side. In FIG. 2 this isindicated by means of straight arrows. Furthermore, in FIG. 2 thesurface 15 of the movable element 3 facing the light guide plate 2 andthe surface 17 of the movable element 3 facing the second plate 4 areindicated.

In FIG. 3 the solidified polymeric layer 36 is a glassy amorphous layer.The solidified polymeric layer 36 may also be a crystalline polymericlayer or a mixture of a glassy amorphous layer and a crystallinepolymeric layer. Examples of these layers are a parylene,polymethylmethacrylate, fluoropolymer and polyimide layer. Also across-linked polymer layer with mechanical properties equivalent tothose of a glassy amorphous or crystalline polymeric layer can be used.The thickness of the solidified polymeric layer 36 is preferably between0.5 and 3 micrometer, with a most preferred range being between 1 and 2micrometer.

In FIG. 3 the inorganic particles 19 are TiO2 particles. The inorganicparticles 19 may alternatively be BN, ZrO2, SiO2, Si3N4 and Al2O3particles. Some inorganic particles 19 are partly embedded in thesolidified polymeric layer 36, forming inorganic protrusions 24 at thesurface 15 of the polymeric foil 30 facing the light guide plate 2. Inthe layer shown, other inorganic particles 19 are entirely embeddedwithin the bulk of the polymeric foil 30. These are referred to asscattering particles 35 present to scatter light out of the polymericfoil 30. It is even possible that the inorganic particles 19 forming theinorganic protrusions 24 are of another size or material than thescattering particles 35. The average size of the scattering particles 35is preferably between 200 and 400 nm. The concentration of scatteringparticles 35 is in the range from 1 to 50 percent by volume of the foil.Preferably the concentration is in between 1 and 25 percent by volume ofthe foil. Preferably the difference in index of refraction between thesolidified polymeric layer 36 and the scattering particles 35 is largerthan 0.1. For smaller differences the scattering efficiency of thescattering particles 35 is rather low. Good scattering results areobtained when the index of refraction is higher than 0.5. Preferredmaterials for the scattering particles 35 are TiO2, BN, and Al2O3, sincethese materials are practically colorless. The index of refraction ofthe solidified polymeric layer 36 is preferably close, differing lessthan approximately 0.2, to the index of refraction of the material ofthe light guide plate 2. In this case, the reflection at the contactsurface between the light guide plate 2 and the movable element 3 issmall. A conductive layer 33, for instance an indium tin oxide layer, ispresent to apply a voltage to the movable element.

FIG. 4 a shows schematically the initial situation, FIG. 4 b shows theresult of step a), FIG. 4 c shows the result of step b), FIG. 4 d showsthe result of step c) and FIG. 4 e shows the result of step d). In stepa) the inorganic particles 19 are partly embedded into a release layer32 which covers a substrate 31. The substrate 31 is for example a glassplate 1 mm thick. The glass plate can be cleaned before it is coveredwith a release layer 32. A product 37 having a rough surface isobtained. In step b) the product 37 is covered with a layer 18 ofpolymeric material, thereby partially embedding the inorganic particles19 within the layer 18 of polymeric material. Subsequently, in step c)the layer 18 of polymeric material is solidified, resulting in asolidified polymeric layer 36, to obtain the polymeric foil 30. Byremoving the release layer 32 in step d), the polymeric foil 30, havinga surface with a roughness brought about by the partially embeddedinorganic particles 19, also referred to as inorganic protrusions 24, isset free from the substrate 31.

The step of embedding inorganic particles 19 partly into the releaselayer 32 can be performed by using the release layer 32 in a relativelysoft viscous state. If the release layer 32 is not in a relatively softviscous state already it has to be brought into a relatively softviscous state. Softening the release layer 32 to bring it into arelatively soft viscous state can be obtained by raising the temperatureof the release layer 32 above the softening temperature of the releaselayer 32. Another way of softening the release layer 32 to bring it intoa relatively soft viscous state is by bringing the release layer 32 intocontact with a material that softens the release layer 32. An example isa release layer 32 that contains organic material that is soluble in asolvent, for instance a release layer 32 containing water-solubleorganic material. Then the release layer 32 can be brought into arelatively soft viscous state by exposure of the release layer 32 tomoist air. Preferably, the release layer 32 contains polyvinyl alcohol,which can be deposited on the substrate 31 e.g. by spinning a polyvinylalcohol solution in water as a polyvinyl alcohol/water film across thesubstrate 31 followed by drying.

The preferred thickness of the release layer 32 is in between 5 and 100nm, with inorganic particles 19 being used having a diameter that is atleast as large as the thickness of the release layer 32. Preferably, theinorganic particles 19 have a diameter between 100 and 1000 nm.

Deposition of the inorganic particles 19 can be performed from anaerosol phase. This results in a homogeneous deposition of the inorganicparticles 19. Furthermore, it is an environmentally friendly processstep. Electrostatic deposition of inorganic particles 19 on the releaselayer involves electrostatic charging of the classified inorganicparticle aerosol, the transport of the charged inorganic particleaerosol towards the release layer 32, and electrostatic deposition ofthe charged inorganic particle aerosol onto the release layer 32 underthe influence of an electrostatic potential difference between apositioned electrode and the substrate 31. In FIG. 5 a definedelectrostatic potential can be applied to the substrate 31 as thesubstrate 31 used contains a conductive layer 34. The conductive layer34 is present in between the substrate 31 and the release layer 32 inFIG. 5 a, whereas in FIG. 5 b the conductive layer 34 is present at thesurface of the substrate 31 facing away from the release layer 32.Furthermore, after deposition of the inorganic particles 19 from anaerosol phase, a product 37 having a rough surface is obtained. In FIG.6 a the result of step a), and in FIG. 6 b the result after a subsequentdipping process involving the immersion of the product 37 into a dippingliquid followed by the withdrawal of the product 37 from the dippingliquid are shown schematically. The process described results in aclustering of inorganic particles 19 on the release layer 32, leading toan increase of the inorganic particle 19 volume fraction in thedeposited inorganic particle 19 layer. An example of a preferred dippingliquid is heptane when the release layer 32 material is polyvinylalcohol and the inorganic particles 19 are TiO₂.

In step b) the product 37 is covered with a layer of polymeric material18 having the inorganic particles 19 partly embedded therein. Theinorganic particles 19 that are partly embedded in the release layer 32are also partly embedded in the polymeric material. If the polymericmaterial is parylene, the solidifying process in step c) occurssimultaneously with the parylene deposition process in step b). Ifpolymethylmethacrylate, some fluoropolymers, or polyimide is used as thepolymeric material and applied on the product 37 from a polymer solutionin a solvent as a polymer/solvent film by means of a wet coating methodsuch as spin coating, the solidifying process occurs during the processof removing the solvent from the polymer/solvent film and during apossible additional thermal curing step at an elevated temperature.

The inorganic particles 19 that are partly embedded in the release layer32 are also partly embedded in the solidified polymeric layer 36.

In step d) the release layer 32 is removed to obtain the polymeric foil30 having a surface with a roughness brought about by the partlyembedded inorganic particles 19. Removing the release layer 32 can beperformed by dissolving the release layer 32 in a solvent. A furtherresult is that the polymeric foil 30 is released from the substrate 31.A polyvinyl alcohol release layer 32 can be removed by dissolving inwater.

In FIG. 7 a the result of step a), in FIG. 7 b the result of depositinga conductive layer 33, in FIG. 7 c the result of step b) and in FIG. 7 dthe result of step c) is shown. A conductive layer 33 is depositedbefore a layer 18 of polymeric material is deposited. In FIG. 8 a theresult of step a), in FIG. 8 b the result of step b), in FIG. 8 c theresult of step c) and in FIG. 8 d the result of depositing a conductivelayer 33 is shown. A conductive layer 33 is deposited after a layer 18of polymeric material is deposited and solidified. After removing therelease layer 32, both polymeric foils contain an electrode formed bythe conductive layer 33. The conductive layer 33 is for instance aconductive indium tin oxide layer. The thickness is preferably about 30nm.

In FIG. 9 both ways of depositing a conductive layer 33 are applied inone process, thereby obtaining a polymeric foil 30 having a conductivelayer 33 at both surfaces. In FIG. 9 a the result of step a), in FIG. 9b the result of depositing a first conductive layer 33, in FIG. 9 c theresult of step b), in FIG. 9 d the result of step c) and in FIG. 9 e theresult of depositing a second conductive layer 33 is shown.

1. A method of manufacturing a polymeric foil (30) having partlyembedded inorganic particles (19), the polymeric foil (30) beingsuitable for use as a movable element (3) in a display panel (21),comprising the steps of a) embedding inorganic particles (19) partlyinto a release layer (32) which covers a substrate (31), therebyobtaining a product (37) having a rough surface, b) covering the product(37) with a layer (18) of polymeric material, thereby partiallyembedding the inorganic particles within the layer (18) of polymericmaterial, c) solidifying the layer (18) of polymeric material to obtainthe polymeric foil (30), and d) removing the release layer (32) to setfree the polymeric foil (30) having a surface with a roughness broughtabout by the partly embedded inorganic particles (19).
 2. A method asclaimed in claim 1, characterized in that the release layer (32) used isbrought into a relatively soft viscous state for embedding inorganicparticles (19) partly into the release layer (32).
 3. A method asclaimed in claim 2, characterized in that the release layer (32) isbrought into a relatively soft viscous state by bringing the releaselayer (32) into contact with a material that is a solvent for therelease layer (32).
 4. A method as claimed in claim 3, characterized inthat the release layer (32) used contains water-soluble organicmaterial.
 5. A method as claimed in claim 4, characterized in that therelease layer (32) is brought into a relatively soft viscous state byexposure of the release layer (32) to moist air.
 6. A method as claimedin claim 1, characterized in that the release layer (32) used has athickness between 5 and 100 nm, and the inorganic particles (19) usedhave a diameter larger than a thickness of the release layer (32).
 7. Amethod as claimed in claim 1, characterized in that in step a) theinorganic particles (19) are deposited from an aerosol phase.
 8. Amethod as claimed in claim 7, characterized in that the substrate (31)used has a conductive layer (34).
 9. A method as claimed in claim 7,characterized in that between step a) and step b) the product (37) isimmersed and subsequently withdrawn from a liquid for increasing thevolume fraction of the inorganic particles (19) on the release layer(32).
 10. A method as claimed in claim 1, characterized in that theproduct (37) and/or the polymeric foil (30) is covered with a conductivelayer (33) prior to performing step d).